Degenerate birdcage coil and transmit/receive apparatus and method for same

Abstract

A birdcage coil ( 16 ) used in conjunction with a magnetic resonance imaging apparatus includes a first conductive loop ( 81, 581 ), a second conductive loop ( 82, 582 ), and a plurality of first conductor rungs ( 80, 580 ) disposed between the first and second conductive loops. A third conductor ( 83, 83″, 583 ) is coupled to the second conductive loop at resonance frequencies, such as by second conductor rungs ( 84, 84″, 584 ). The birdcage coil also includes switches ( 590 ) for switching the birdcage coil at least among: 1) an RF transmit mode to operate as an RF transmit coil; and 2) an RF receive mode to operate as an RF receive coil.

1. A birdcage coil system for use in conjunction with a magnetic resonance apparatus, the birdcage coil system comprising:
 a birdcage coil tuned to degeneracy the coil including:
 a first conductive loop, 
 a second conductive loop, and 
 a plurality of first conductor rungs disposed between the first and second conductive loops and in electrical connection therewith; and 
 
 a switching system which switches the birdcage coil at least between:
 an RF transmit mode, and 
 an RF receive mode, 
 
 the switching system including:
 a plurality of RF transmit feed points in electrical connection with the first conductive loop for feeding RF transmit signals to the coil; 
 a plurality of transmit PIN diodes for coupling RF transmit feeds to the feed points; 
 a plurality of RF receive take-off points disposed across matching capacitors; 
 a plurality of matching PIN diodes arranged in parallel with the matching capacitors; and 
 a plurality of cage DC bias inputs in electrical connection with the transmit and matching diodes for biasing the transmit and matching PIN diodes. 
 
 
   
   
     2. A birdcage coil system as set forth in  claim 1  wherein:
 in the transmit mode the birdcage coil is adapted to operate as a quadrature RF transmit coil. 
 
   
   
     3. A birdcage coil system as set forth in  claim 1  wherein:
 the birdcage coil is adapted to operate as a parallel imaging RF coil. 
 
   
   
     4. A birdcage coil system as set forth in  claim 1  wherein:
 in transmit mode, said transmit and matching PIN diodes arc forward biased by cage DC bias whereby the transmit PIN diodes provide connections for the transmit signals from an RF transmitter to pass to the birdcage coil and the matching PIN diodes short-out the matching capacitor and prevent RF signal take-off. 
 
   
   
     5. A birdcage coil system as set forth in  claim 4  wherein:
 in the receive mode, said transmit and matching PIN diodes are reverse biased by cage DC bias whereby the transmit PIN diodes disconnect the birdcage coil from the RF transmitter and the matching PIN diodes allow RF signal take-off. 
 
   
   
     6. A magnetic resonance imaging system comprising: a main magnet generating a temporally constant magnetic field;
 magnetic field gradient coils selectively imposing selected magnetic field gradients on the temporally constant magnetic field; and 
 the birdcage coil of  claim 1 . 
 
   
   
     7. A birdcage coil system for use in conjunction with a magnetic resonance apparatus, the birdcage coil system comprising:
 a birdcage coil tuned to degeneracy, the coil including:
 first conductive loop, 
 a second conductive loop, and 
 a plurality of first conductor rungs disposed between the first and second conductive loops and in electrical connection therewith; and 
 
 switching elements switch the birdcage coil at least between:
 an RF transmit mode, and 
 an RF receive mode, 
 a plurality of feed points on the first conductive loop, for feeding RF transmit signals to the coil, 
 
 the switching means elements further including:
 a plurality of preamp PIN diodes in electrical connection with corresponding RF receive pre-amplifiers, the receive pre-amplifiers being connected with take-off points on one of the conductive loops; 
 a plurality of preamp DC bias inputs in electrical connection with the preamp PIN diodes for biasing the preamp diodes and shorting-out the RF receive pre-amplifiers. 
 
 
   
   
     8. A birdcage coil system as set forth in,  claim 7  wherein:
 the switching elements are further adapted to switch the birdcage coil to a decoupled mode in which the cage DC bias reverse biases the transmit and matching PIN diodes and the preamp DC bias forward biases the preamp PIN diode whereby the RF coil is decoupled from the magnetic resonance apparatus. 
 
   
   
     9. A birdcage coil system for use in conjunction with a magnetic resonance imaging apparatus, the birdcage coil system comprising:
 a birdcage coil tuned to degeneracy, the coil including:
 a first conductive loop, 
 a second conductive loop, 
 a plurality of first conductor rungs disposed between the first and second conductive loops and in electrical connection therewith, 
 a third conductor coupled at radio frequencies with the second conductive loop; 
 a plurality of second conductor rungs disposed between the second conductive loop and third conductor and in electrical connection therewith, 
 wherein reactances of at least one of the third conductor and the plurality of second conductor rungs are selected to decouple next-neighbor meshes of the birdcage coil; and 
 
 a switching means for switching the birdcage coil at least between:
 an RF transmit mode, and 
 an RF receive mode in which in the birdcage coil is adapted to operate as a phased array RF receive coil. 
 
 
   
   
     10. A birdcage coil system as set forth in  claim 9 , wherein the birdcage coil is a degenerate birdcage coil defining a plurality of meshes that are decoupled at least from nearest neighbor and next-nearest neighbor meshes, and the switching means comprises:
 a plurality of transmit/receive switches connected with the meshes to independently operate the plurality of decoupled meshes. 
 
   
   
     11. A birdcage coil system as set forth in  claim 10 , wherein each of the transmit/receive switches comprises:
 a mesh coupling connecting the transmit/receive switch with the corresponding decoupled mesh; 
 a receive circuit communicating with the mesh coupling; and 
 a transmitter input; and 
 a means for selectively connecting the transmitter input with the mesh coupling. 
 
   
   
     12. A birdcage coil as set forth in  claim 9  wherein:
 the first and second loops are arranged on opposite ends of the first conductor rungs, said plurality of first conductive rungs making electrical connections with the first and second conductive loops such that said first and second conductive loops have first and second segments thereof situated between the electrical connections of neighboring first conductive rungs and a pair of neighboring first conductive rungs and the first and second loop segments situated between the electrical connections with the pair define a mesh; and 
 the birdcage further comprising:
 first rung reactances are disposed within the first conductive rungs; 
 first loop reactances are disposed within the first loop segments; and 
 second loop reactances are disposed within the second loop segments. 
 
 
   
   
     13. A birdcage coil as set forth in  claim 12  further comprising:
 a plurality of second conductor rungs extending between the second conductor loop and the third conductor such that the third conductor is arranged on a side of the second loop opposite the first loop, said plurality of second rungs making electrical connections with the second conductive loop and the third conductor such that said third conductor has segments thereof situated between the electrical connections of neighboring second members. 
 
   
   
     14. A birdcage coil as set forth in  claim 13  wherein:
 the second rungs are equal in number to the first rungs, and the first same locations. 
 
   
   
     15. A birdcage coil as set forth in  claim 14  wherein the first and second rungs are formed to be single conductive rungs that have an electrical intersection with the second loop and ends which make electrical connections with the first loop and the third conductor, respectively. 
   
   
     16. A birdcage coil as set forth in  claim 15  further comprising:
 second rung reactances disposed within the second rungs. 
 
   
   
     17. A birdcage coil as set forth in  claim 16  wherein:
 the first rung, second rung, first loop, and second loop reactances comprise first rung capacitors, second rung capacitors, first loop capacitors, and second loop capacitors, respectively. 
 
   
   
     18. A birdcage coil as set forth in  claim 9 , wherein one of the second conductive loop and the third conductor lies inside of the other. 
   
   
     19. A birdcage coil as set forth in  claim 18 , wherein the second conductor loop and the third conductor are coplanar. 
   
   
     20. A birdcage coil as set forth in  claim 9 , wherein the third conductive loop is inductively coupled with the second conductive loop. 
   
   
     21. A birdcage coil as set forth in  claim 20 , wherein the third conductor includes inductances selected to decouple next-nearest neighbor meshes of the birdcage coil. 
   
   
     22. A birdcage coil as set forth in  claim 9 , wherein reactances of the conductor rungs, conductive loops, and conductors are selected such that the birdcage coil is a degenerate birdcage coil having nearest neighbor and next-nearest neighbor meshes substantially decoupled. 
   
   
     23. A birdcage coil as set forth in  claim 9 , wherein the birdcage coil is a degenerate birdcage coil defining a plurality of meshes that are decoupled at least from nearest neighbor and next-nearest neighbor meshes, the birdcage coil further comprising:
 a plurality of transmit/receive switches connected with the meshes to independently operate the plurality of decoupled meshes as at least one of radio frequency transmitters and radio frequency receivers. 
 
   
   
     24. A birdcage coil as set forth in  claim 23 , wherein the transmit/receive switches are adapted to operate the birdcage coil as at least one of:
 a volume resonator, 
 a transmit SENSE coil array, 
 a receive SENSE coil array, and 
 a parallel imaging coil array. 
 
   
   
     25. A birdcage coil system for use in conjunction with a magnetic resonance imaging apparatus, the birdcage coil system comprising:
 a birdcage coil tuned to degeneracy, the coil including:
 a first conductive loop, the first conductive loop being interrupted by a plurality of matching capacitors, 
 a second conductor loop, 
 a plurality of first conductor rungs disposed between the first and second conductive loops and in electrical connection therewith, 
 a third conductive loop capacitively coupled to the second conductive loop, 
 a plurality of second conductor rungs disposed between the second and third conductive loops and in electrical connection therewith, 
 a plurality of feed points for feeding RF transmit signals to the coil from an RF transmitter in a transmit mode, 
 a plurality of take-off points defined across the matching capacitors from which received signals are conveyed to a plurality of preamplifiers in a receive mode, and 
 wherein reactances of at least one of third conductive loop and the plurality of second conductor rungs are selected to decouple next-neighbor meshes of the birdcage coil. 
 
 
   
   
     26. A birdcage coil system as set forth in  claim 25 , further including:
 a switching system which switches the coil between a transmit mode and a receive mode, the switching system including:
 a plurality of transmit PIN diodes which couple the RF transmit signals to the feed points; 
 a plurality of matching PIN diodes arranged in parallel with the matching capacitors; 
 a plurality of preamp PIN diodes in electrical connection with the plurality of preamp PIN diodes; 
 
 a DC bias source which:
 in a transmit mode, biases the transmit PIN diodes to pass the RF transmit signals to the feed points from the RF transmitter, biases the matching PIN diodes to short the matching capacitors, and biases the preamp PIN diodes to prevent RF signals from being taken off and conveyed to the preamplifiers, and 
 in a receive mode, biases the transmit PIN diodes to disconnect the feed points from the RF transmitter and biases the matching and preamp PIN diodes to allow RF signals to be taken off and supplied to the preamplifiers.